The use of filler wire has come into wide acceptance in the field of electric arc welding. The wire serves as a consumable electrode which is continuously provided to an electric arc that melts the wire and deposits it at a welding bead. The use of filler wire has contributed to the development of automated welding equipment, particularly in the field of pipeline welding.
Existing automated welding systems have been successful in heavy welding applications, such as the welding of relatively large diameter pipelines. However, in lightweight applications, such as robotic welding, conventional wire feed systems have been less successful. A particular problem in lightweight, wire-feed welding systems is the difficulty in accurately positioning the wire at the welding bead. The filler wire is wrapped around a spool which applies a cast to the wire and the cast varies according to the diameter of the wire around the spool. In a conventional wire feed system the wire is directed through a bouden tube which feeds the wire to the arc. The size of the bouden tube must be made as small as possible to try to accurately position the wire. However, as the tube is made closer to the diameter of the wire, the friction of the tube increases thus making it more difficult to drive the wire through the tube to the welding arc. In keeping the friction to a low enough level, there must necessarily be space for movement of the wire. The wire is then free to twist about within the tube and this permits the wire to move erratically as it is applied to the arc. Such movement of the filler wire at the arc can offset the welding bead sufficiently far to cause a defective weld, which can result in rejection of the product.
A further difficulty with conventional wire feed systems is the excessive time and complexity involved in feeding the wire into the drive system. In conventional systems, various portions of the wire feed assembly must be opened or disassembled to allow the wire to be inserted and clamped to the drive mechanism. Since this must be done each time a spool of wire is replaced for the welder, a substantial amount of time can be wasted, especially in high production situations.
In view of the above problems with wire feed systems, there exists a need for a new wire feed mechanism which can drive the wire and position it with a high degree of accuracy and can load the wire rapidly without the need for opening the apparatus or removing components.